Inconsistent menu visibility for Mobile Safari devices

Description

When using a device running Mobile Safari the 'Add New' menu under 'Media' is not shown (as iOS devices typically can't upload files). However this is the only place this menu is hidden. This menu is still shown in the admin toolbar and the 'Add New' link is still shown in the Media Library.

Some mobile devices indeed have the capability to upload files. With wp_is_mobile(), the check isn't limited to Safari. Since [20417], it's no longer possible to upload files using Opera Mini on Windows Mobile.